You're basically given a clue on the website or app to find a container in a real life location and have to find it. (They're usually well hidden from the public eye) Once you do, you usually sign your name on a slip of paper in the container and if there are items inside you take one and leave one. There are over 2 million of these located across the globe - chances are your neighborhood has a bunch. I've found about 30 so far. Latest one was under a lamp post in my local taco Bell.